The field of the present disclosure relates generally to turbine engines, and more particularly to hot gas path components having near wall cooling features.
Gas turbine systems are widely utilized in fields such as power generation. A conventional gas turbine system includes a compressor, a combustor, and a turbine. During operation of the gas turbine system, various hot gas path components in the system are subjected to high temperature flows, which can cause the hot gas path components to fail. Since higher temperature flows generally result in increased performance, efficiency, and power output of the gas turbine system and are thus desired in a gas turbine system, the hot gas path components that are subjected to high temperature flows must be cooled to allow the gas turbine system to operate with flows at increased temperatures.
As the maximum local temperature of the hot gas path components approaches the melting temperature of the hot gas path components, forced air cooling becomes necessary. For this reason, airfoils of gas turbine buckets and nozzles often require complex cooling schemes in which air, typically bleed air, is forced through internal cooling passages within the airfoil and then discharged through cooling holes at the airfoil surface to transfer heat from the hot gas path component. Cooling holes can also be configured so that cooling air serves to film cool the surrounding surface of the hot gas path component.
Various strategies are known in the art for cooling the hot gas path components that are subjected to high temperature flows. For example, a series of internal cooling passages may be formed in a hot gas path component to facilitate cooling the hot gas path components. Buckets and nozzles formed by casting processes require cores to define the internal cooling passages. The cores and their potential for shifting during the casting process limits the extent to which a conventional casting process can locate a cooling passage in proximity to an exterior surface of the hot gas path component. As a result, cooling passages are typically about 0.1 inch (about 2.5 millimeters) or more below a base metal surface of a cast turbine bucket or nozzle. However, the heat transfer efficiency could be significantly increased if the cooling passages could be placed closer to the surface. The smaller cooling passages, or micro-channels, present a considerable fabrication challenge for cores and castings, which can significantly increase the manufacturing cost of the hot gas path components using such known near wall cooling systems.